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[perl #132461] \&foo deparsing is overlong

From:
Zefram
Date:
November 17, 2017 10:21
Subject:
[perl #132461] \&foo deparsing is overlong
Message ID:
rt-4.0.24-27532-1510914056-826.132461-75-0@perl.org
# New Ticket Created by  Zefram 
# Please include the string:  [perl #132461]
# in the subject line of all future correspondence about this issue. 
# <URL: https://rt.perl.org/Ticket/Display.html?id=132461 >



This is a bug report for perl from zefram@fysh.org,
generated with the help of perlbug 1.40 running under perl 5.27.5.


-----------------------------------------------------------------
[Please describe your issue here]

$ perl -MO=Deparse -e 'use strict; print \&foo'
use strict;
print \&main::foo;
-e syntax OK

The deparsing unnecessarily includes package qualification.  The deparser
generally avoids unnecessary qualification, for example it doesn't qualify
the corresponding glob ref.  So this seems undesirable behaviour, which
should probably be changed.

The conditions for this to happen are an "&foo" reference to a sub,
where the sub is in the current package, the sub is not being called,
"use strict 'vars'" is in effect, and no lexical sub of the same name
is in scope.  It has not always been this way: prior to Perl 5.21.7 the
package qualification was not included.  Crucially, this changed at the
same time as a related bugfix: in the early days of lexical subs the
deparser would emit "&foo" for a package sub even if it was shadowed by
a lexical sub, then in 5.21.7 the deparser started package-qualifying
shadowed subs.	So the present behaviour seems to be a mistake, arising
from treating subs just like scalars in the relationship between package
and lexical namespaces.  It was correct to look for lexical shadowing,
but undesirable to suppose that "use strict 'vars'" would apply to them.

Recently the deparsing of the affected case was accidentally
`fixed' to the short form (without reintroducing any shadowing bug)
by commit dd6661605fe0a54c602f2e55f875acfdcd330b79.  However, this
broke a test in Devel::Cover's test suite.  The test is sensitive to
non-guaranteed details of deparsing, and has a mechanism for updating
expectations when the deparsing changes, which had already been applied
to change the expectation in 5.22.  Because breaking this test wasn't
intentional, the deparsing was changed back to the long form in commit
257296eb9dbe871f5ba95266c9a55fa0feead316 to resolve the BBC.  This ticket
is about *intentionally* fixing it.

To fix the deparsing, revert the code part of commit
257296eb9dbe871f5ba95266c9a55fa0feead316, and update the "\&foo" and
"exists(&foo)" tests added by that commit.  The change will break
Devel::Cover, so best make sure pjcj is ready first.

[Please do not change anything below this line]
-----------------------------------------------------------------
---
Flags:
    category=library
    severity=low
    module=B::Deparse
---
Site configuration information for perl 5.27.5:

Configured by zefram at Fri Oct 20 23:24:00 BST 2017.

Summary of my perl5 (revision 5 version 27 subversion 5) configuration:
   
  Platform:
    osname=linux
    osvers=3.16.0-4-amd64
    archname=x86_64-linux-thread-multi
    uname='linux barba.rous.org 3.16.0-4-amd64 #1 smp debian 3.16.43-2+deb8u2 (2017-06-26) x86_64 gnulinux '
    config_args='-des -Dprefix=/home/zefram/usr/perl/perl_install/perl-5.27.5-i64-f52 -Duselargefiles -Dusethreads -Uafs -Ud_csh -Uusesfio -Uusenm -Duseshrplib -Dusedevel -Uversiononly -Ui_db'
    hint=recommended
    useposix=true
    d_sigaction=define
    useithreads=define
    usemultiplicity=define
    use64bitint=define
    use64bitall=define
    uselongdouble=undef
    usemymalloc=n
    default_inc_excludes_dot=define
    bincompat5005=undef
  Compiler:
    cc='cc'
    ccflags ='-D_REENTRANT -D_GNU_SOURCE -fwrapv -fno-strict-aliasing -pipe -fstack-protector-strong -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64 -D_FORTIFY_SOURCE=2'
    optimize='-O2'
    cppflags='-D_REENTRANT -D_GNU_SOURCE -fwrapv -fno-strict-aliasing -pipe -fstack-protector-strong -I/usr/local/include'
    ccversion=''
    gccversion='4.9.2'
    gccosandvers=''
    intsize=4
    longsize=8
    ptrsize=8
    doublesize=8
    byteorder=12345678
    doublekind=3
    d_longlong=define
    longlongsize=8
    d_longdbl=define
    longdblsize=16
    longdblkind=3
    ivtype='long'
    ivsize=8
    nvtype='double'
    nvsize=8
    Off_t='off_t'
    lseeksize=8
    alignbytes=8
    prototype=define
  Linker and Libraries:
    ld='cc'
    ldflags =' -fstack-protector-strong -L/usr/local/lib'
    libpth=/usr/local/lib /usr/lib/gcc/x86_64-linux-gnu/4.9/include-fixed /usr/include/x86_64-linux-gnu /usr/lib /lib/x86_64-linux-gnu /lib/../lib /usr/lib/x86_64-linux-gnu /usr/lib/../lib /lib
    libs=-lpthread -lnsl -ldb -ldl -lm -lcrypt -lutil -lc
    perllibs=-lpthread -lnsl -ldl -lm -lcrypt -lutil -lc
    libc=libc-2.19.so
    so=so
    useshrplib=true
    libperl=libperl.so
    gnulibc_version='2.19'
  Dynamic Linking:
    dlsrc=dl_dlopen.xs
    dlext=so
    d_dlsymun=undef
    ccdlflags='-Wl,-E -Wl,-rpath,/home/zefram/usr/perl/perl_install/perl-5.27.5-i64-f52/lib/5.27.5/x86_64-linux-thread-multi/CORE'
    cccdlflags='-fPIC'
    lddlflags='-shared -O2 -L/usr/local/lib -fstack-protector-strong'


---
@INC for perl 5.27.5:
    /home/zefram/usr/perl/perl_install/perl-5.27.5-i64-f52/lib/site_perl/5.27.5/x86_64-linux-thread-multi
    /home/zefram/usr/perl/perl_install/perl-5.27.5-i64-f52/lib/site_perl/5.27.5
    /home/zefram/usr/perl/perl_install/perl-5.27.5-i64-f52/lib/5.27.5/x86_64-linux-thread-multi
    /home/zefram/usr/perl/perl_install/perl-5.27.5-i64-f52/lib/5.27.5

---
Environment for perl 5.27.5:
    HOME=/home/zefram
    LANG (unset)
    LANGUAGE (unset)
    LD_LIBRARY_PATH (unset)
    LOGDIR (unset)
    PATH=/home/zefram/usr/perl/perl_install/perl-5.27.5-i64-f52/bin:/home/zefram/usr/perl/util:/home/zefram/pub/x86_64-unknown-linux-gnu/bin:/home/zefram/pub/common/bin:/usr/bin:/bin:/usr/local/bin:/usr/games
    PERL_BADLANG (unset)
    SHELL=/usr/bin/zsh




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